FIG. 8 is a schematic constitutional view showing the conventional laser material processing apparatus for drilling.
In FIG. 8, reference numeral 1 denotes a workpiece such as a printed board, 2 denotes a laser beam for drilling the workpiece 1 to make a via hole or through hole, 3 denotes a laser oscillator for oscillating the laser beam 2, 4 denotes a plurality of mirrors for reflecting the laser beam 2 along the optical path, 5 and 6 denote a galvano scanner for scanning the laser beam 2, 7 denotes an fθ lens for focusing the laser beam 2 on the workpiece 1, and 8 denotes an XY stage for moving the workpiece 1.
In the typical laser material processing apparatus for drilling, the laser beam 2 oscillated from the laser oscillator 3 is conducted via a necessary mask and the mirrors 4 to the galvano scanners 5, 6 and focused via the fθ lens 7 at a predetermined position of the workpiece 1 by controlling the deflection angle of the galvano scanners 5, 6.
The deflection angle of the galvano scanners 5, 6 via the fθ lens 7 is limited to a range of 50 mm square, for example. Therefore, the laser beam 2 is focused at the predetermined position of the workpiece 1 by controlling the XY stage 8 as well, thereby allowing the workpiece 1 to be machined in a broader range.
Herein, the productivity of the laser material processing apparatus is closely related with the drive speed of the galvano scanners 5, 6 and the processing area of the fθ lens 7.
To improve the drive speed of the galvano scanner, it is effective to change the design of an optical system by reducing the mass of a galvano mirror fixed to the rotation shaft of the galvano scanner and driven by controlling the deflection angle, or varying the distance between the galvano scanners 5, 6 and the fθ lens 7, and to reduce the deflection angle while the processing range is maintained. However, if the mirror diameter of the galvano scanner is made smaller to reduce the mass of the galvano mirror, the laser beam 2 has its peripheral portion intercepted by a mask in passing through the mask, and the diameter once reduced, but the laser beam 2 is broadened in diameter due to diffraction after passing through the mask, and has a larger diameter than the galvano mirror when arriving at the galvano mirror of the galvano scanner 5, 6, causing a part of the laser beam 2 to get out of the galvano mirror, so that an image of the mask is not correctly transferred onto the workpiece 1, whereby the micro hole fabrication is not made.
Also, the deflection angle of the galvano scanners is reduced while the processing range is maintained in such a way as to change the optical design, including changing the positional relation between the fθ lens and the galvano scanners. However, it takes a lot of time to design, and it is required to change the specification of the very expensive fθ lens or the design of the overall optical system, whereby it was difficult to improve the productivity easily and cheaply with a single beam.
A laser material processing apparatus of the previously described type intended to improve the productivity was disclosed in JP-A-11-314188, for example.
FIG. 9 is a schematic constitutional view of the laser material processing apparatus as disclosed in JP-A-11-314188.
In FIG. 9, reference numeral 9 denotes a workpiece, 10 denotes a mask, 11 denotes a half-mirror for separating a laser light, 12 denotes a dichroic mirror, 13a denotes a laser beam reflected from the half-mirror, 13b denotes a laser beam transmitted through the half-mirror and reflected from the dichroic mirror, 14 and 15 denote the mirrors, 16 denotes an fθ lens for focusing the laser beams 13a and 13b onto the workpiece 9, 17 and 18 denote galvano scanners for conducting the laser beam 13a to a processing area A1, 19 and 20 denote galvano scanners for conducting the laser beam 13b to a processing area A2, and 21 denotes an XY stage for moving each part of the workpiece to the processing area A1 or A2.
The laser material processing apparatus as shown in FIG. 9 separates the laser light passing through the mask 10 via the half-mirror 11 into plural beams, conducts the separated laser beams 13a and 13b to a plurality of galvano scanner systems arranged on the incident side of the fθ lens 16, and scans the laser beams 13a and 13b with the plurality of galvano scanner systems to be applied to the divided processing areas A1 and A2.
The separated laser beam 13a is introduced via the first galvano scanner system 17, 18 into a half area of the fθ lens 16. Also, the other separated laser beam 13b is introduced via the second galvano scanner system 19, 20 into a remaining half area of the fθ lens 16. The first and second galvano scanner systems are arranged in symmetry about the central axis of the fθ lens 16, whereby the half parts of the fθ lens 16 are employed at the same time to improve the productivity.
However, in the apparatus as disclosed in JP-A-11-314188, the first galvano scanner system 17, 18 and the second galvano scanner system 19, 20 scan the laser beams, into which laser light is separated via the half mirror 11, to be applied on the processing areas A1 and A2 that are divided. Therefore, a dispersion in the quality of processed holes is likely to occur due to a difference between reflection from and transmission through the half mirror 11 between the laser beams 13a and 13b, into which laser light is separated by the half mirror 11.
For example, when there is an energy difference between the separated laser beams 13a and 13b, a difference in the hole diameter or hole depth of the processed holes is likely to occur on the workpiece 9. Therefore, there is the possibility that the strict requirements for processing the hole are not satisfied in terms of the dispersion in the hole diameter.
Herein, when the laser beam 13a has a higher energy than the laser beam 13b, it is required to adjust the energy of laser beam 13b to be decreased by further adding an expensive optical component such as an optical attenuator on the optical path of laser beam 13b. The optical component such as the optical attenuator must be produced in the specification of removing the energy at a certain percentage. For example, when the specification of removing the energy of 5% and the specification of removing the energy of 3% are required, two kinds of optical attenuator are produced. Thereby, the optical attenuator is prepared in a few kinds of specification, and exchanged every time the energy difference is adjusted.
Also, in the optical path constitution as shown in FIG. 9, there was a problem that the optical path lengths of laser beams 13a and 13b, into which laser light is separated after passing through the mask 10, up to the workpiece 9 are different, so that the strict beam spot diameters on the workpiece 9 are different.
Moreover, the fθ lens 16 is equally divided, and the divided processing areas A1, A2 are machined at the same time. Therefore, when the number of processed holes in the processing areas A1 and A2 is greatly varied, or when there is no processed hole of object in either the processing area A1 or A2 such as an end portion of the workpiece, it is not expected to improve the productivity.